Something Wrong?

Hi.

I have noticed some of my fish seeming lethargic at times lately. The issue has been that it is only some of the fish which seem to be acting strangely... My smaller of my two red honey seems to be hiding along the bottom of the tank more and two of my ember tetras have been hovering in the Java fern. I have also lost two guppies recently, however, I think this is because of the fin rot they have had, so not sure if this is related.

With my red honey gourami, I am wondering if the larger of the two is attempting to bubble nest, but is unable to due to the lack of floating plants in my tank or whether it is ill for some reason. The ember tetras behaving differently has made me worry that this may be a disease/stress related issue. There is no discolouration in the fish or anything physically wrong with them, and they seem to be feeding fine and are quite active during feeding time (like magnets to the top of the tank!). As for the guppies, I haven't been able to treat them or anything as my tank currently has bamboo shrimp in, which are sensitive to fish medicines and my spare tank is currently housing some zebra danio who were too stressful for my honey gourami to handle.

I have no idea what is going on and everything with the tank seems fine at the minute and have been stable since the tank was set up. I have recently had to remove some Lysimachia from the tank and have replaced it with a mixture of Echinodorus and Java Fern (starting rotting from the roots and letting loose from the substrate). Not sure whether any of this has been an issue, but am at wits end! Have also started using liquid CO2 to as fertiliser for the plants.

Does anyone have any suggestions?

Thanks!